Comb polymers for improving noack evaporation loss of engine oil formulations

ABSTRACT

A comb polymer can be used for reducing a Noack evaporation loss of a lubricant composition, especially of an engine oil composition. Application of the comb polymer to the lubricant composition can bring about the desired reduction. The comb polymer can include specified amounts of macromonomer and alkyl acrylates. Resulting lubricant compositions can include the comb polymer.

The present invention is directed to selected comb polymers comprisingspecified amounts of macromonomer and alkyl acrylates, theirpreparation, lubricant compositions comprising such comb polymers andtheir use for reducing Noack evaporation losses of lubricantcompositions, especially of engine oil (EO) compositions.

Evaporation losses in lubricant oils are an important topic not onlybecause of their significance on environmental topics, but also becauseof their impact on lubricant performance and formulation regulations. Inmany applications the loss of lubricant due to evaporation can besignificant. At elevated temperatures oils then become more viscousbecause of evaporation. Volatile components of the lubricant may be lostthrough evaporation, resulting in a significant increase in viscosityand a further temperature rise due to higher friction, which in turncauses further oil losses due to evaporation. Volatility of lubricantsis expressed as a direct measure of evaporation losses, for examplemeasured by the Noack method (G. W. Stachowiak, A. W. Batchelor,Engineering Tribology, 4th Edition, p. 37-38, 2013).

Over the years, various research was done on a correlation of lubricantvolatility to engine emissions and oil consumption. It is thereforeknown that reducing lubricant volatility should have a positive impacton both of these important engine performance characteristics. For thisreason lubricant volatility has become and will continue to be animportant specification in modern engine oils (de Paz, E. and Sneyd, C.,“The Thermogravimetric Noack Test: A Precise, Safe and Fast Method forMeasuring Lubricant Volatility,” SAE Technical Paper 962035, 1996).

The contribution of engine oil evaporation to oil consumption wasstudied in detail as it is an important source of hydrocarbon andparticulate emissions in automotive engines. Another negative effectcaused by oil consumption in engines is the increase in oil viscositywhich in turn results in decreased oil circulation and lower fueleconomy. Oil consumption in engines is directly related to physical oilproperties such as engine oil volatility and viscosity. The volatilitydirectly governs the oil evaporation rate from hot surfaces during theengine cycle. Oil evaporating from the piston-ring-liner-system isbelieved to contribute significantly to total oil consumption (Yilmaz,E., Tian, T., Wong, V., and Heywood, J., “An Experimental andTheoretical Study of the Contribution of Oil Evaporation to OilConsumption,” SAE Technical Paper 2002-01-2684, 2002).

This shows the importance of engine oil volatility on modern engine oilperformance. As a result, one specification in engine oil formulationsestablished by the Society of Automotive Engineers (SAE), SAE J300, isthe definition of a maximum Noack evaporation loss of the formulation(Engine Oil Viscosity Classification, J300_201501, Fuels and LubricantsTc 1 Engine Lubrications, SAE International, 2015).

Noack is a frequently used method to measure lubricant volatility.Lubricant manufacturers and users recognize that the operatingconditions of the Noack methods are representative of those experiencedby oils in engines. The Noack volatility of an oil is the weight lost bythe oil when it is heated at 250° C. for 1 hour under a constant airflow. This test, like the engine, constantly exposes the oil to air andthe test temperature is comparable to those around the top piston ringsof engines. The piston ring area may be the main pathway by which oilvolatility impacts emissions and oil consumption. This is due in part tothe high temperatures, but it is also the result of the lubricant'sclose proximity to the combustion chamber and its exhaust valves (dePaz, E. and Sneyd, C., “The Thermogravimetric Noack Test: A Precise,Safe and Fast Method for Measuring Lubricant Volatility,” SAE TechnicalPaper 962035, 1996).

In summary, it is very important to minimize the evaporative loss orNoack of lubricants, especially of lubricants for engines, in order toavoid oil consumption effects like reduced oil circulation and decreasedfuel economy and environmentally problematic emissions.

Evaporation loss in lubricant applications is attributed to theproperties of the base oil used in a lubricating composition. Dependingon the base oils different Noack values are obtained. It was found thatby using ester oils with less volatile components in the lubricant,typically lower Noack values were obtained (Horner, D. (2002), Recenttrends in environmentally friendly lubricants. J. Synthetic Lubrication,18: 327-347).

This literature shows that today it is believed that the evaporationloss of the base oil components influence the Noack values. In contrast,there is very little known about the contribution solid additives mighthave on evaporation loss. There are only very few publicationsdescribing the influence of additives on the evaporative loss inlubricant oils. Bartz (Bartz, W. J. (2000), Influence of viscosity indeximprover, molecular weight, and base oil on thickening, shear stability,and evaporation losses of multigrade oils. Lubrication Science, 12:215-237), for example, describes the influence of the additive amount onevaporative loss, but could not detect a systematic correlation or biginfluence.

In general, it is believed today that evaporative losses in lubricantsare attributed to the base oils. Typically, in an engine oil formulationthe base oil is selected having the lowest volatility obtainable at thenecessary volatility level (Coon, J. and Loeffler, D., “Routes ofcrankcase oil loss,” SAE Technical Paper 590009, 1959).

However, changing the base oil mixture in a lubricating composition toimprove the Noack evaporation loss has limitations, because the criteriahow base oils are selected are manifold and other parameters likeviscometric performance, sulfur content, aromatic content oravailability as well as price play an important role.

Until now it was not possible to reduce the Noack to a minimum value byjust optimizing the base oil mixture. But as Noack becomes more and moreimportant with lower engine oil grades (like 0W8), a solution forimproving Noack has to be found.

Noack is defined as a method to measure evaporation loss of fullyformulated engine oils. By measuring the evaporation loss of singlecomponents like viscosity index (VI) improvers, it was now surprisinglyfound that there is a significant contribution to evaporation loss bythe single components in addition to the base oil mix used in thelubricant. More specifically, it was found that certain types of VIimprovers significantly contribute to the Noack evaporation loss. Thisis unexpected as VI improvers mainly consist of oil (which is needed forthe handling of the VI improver and of which it is known to be a sourceof evaporation loss) and a solid polymer (which should not contribute tothe Noack evaporation loss).

It was now surprisingly found that polyalkyl(meth)acrylate based combpolymers comprising a small amount of alkyl acrylates can contribute toa low Noack evaporation loss of a lubricating composition.

The comb polymer technology in general and their use as viscosity indeximprover is already known (US 2008/0194443, US 2010/0190671 and WO2014/170169), although the effect of the polymer comprising acrylates ascomonomers in combination with low Noack of combs in lubricatingformulations has never been described.

Lubricant properties are typically improved by the addition of additivesto lubricating oils.

U.S. Pat. Nos. 5,565,130 and 5,597,871, for example, disclose using combpolymers comprising polybutadiene-derived macromonomers as viscosityindex improvers. However, no effect on the Noack volatility is disclosedtherein.

WO 2007/003238 A1 describes oil-soluble comb polymers based onpolyolefin-based macromonomers, especially polybutadiene-basedmethacrylic esters, and C1-C10 alkyl methacrylates. The comb polymerscan be used as an additive for lubricant oils, in order to improve theviscosity index and shear stability. However, no effect on the Noackvolatility is disclosed therein.

WO 2009/007147 A1 discloses the use of comb polymers based onpolyolefin-based macromonomers, especially polybutadiene-basedmethacrylic esters, and C1-C10 alkyl methacrylates for improving thefuel consumption of motor vehicles. However, no effect on the Noackvolatility is disclosed therein.

WO 2010/102903 A1 discloses the use of comb polymers as antifatigueadditives for transmission, motor and hydraulic oils. However, no effecton the Noack volatility is disclosed therein.

DE 10 2009 001 447 A1 describes the use of comb polymers for improvingthe load-bearing capacity of hydraulic oils having a high viscosityindex. However, no effect on the Noack volatility is disclosed therein.

WO 2012/025901 A1 (Total) discloses the use of comb polymers inlubricants in combination with particular friction modifiers. However,no effect on the Noack volatility is disclosed therein.

Since the properties of the lubricants disclosed in the prior art arestill unsatisfactory in relation to an improvement of the Noackvolatility, it is the aim of the present invention to provide singlecomponents which contribute significantly to evaporation loss when addedto a base oil used in a lubricating composition.

It was surprisingly found that comb polymers comprising a small amountof esters of (meth)acrylic acid and a hydroxylated hydrogenatedpolybutadiene and a small amount of alkyl acrylates have a positiveimpact on the Noack volatility of a lubricating composition.

DESCRIPTION OF THE INVENTION

A first object of the present invention is therefore directed topolyalkyl(meth)acrylate based comb polymers, comprising the followingmonomers:

-   -   (a) 10 to 25% by weight of esters of (meth)acrylic acid and a        hydroxylated hydrogenated polybutadiene; and    -   (b) 0.5% to 11% by weight, preferably 0.5 to 5% by weight, of        C₄₋₁₈ alkyl acrylates.

A preferred first embodiment is directed to the polyalkyl(meth)acrylatebased comb polymers, comprising the following monomers:

-   -   (a) 10 to 25% by weight of an ester of (meth)acrylic acid and a        hydroxylated hydrogenated polybutadiene;    -   (b) 0.5% to 11% by weight, preferably 0.5 to 5% by weight, of        C₄₋₁₈ alkyl acrylates;    -   (c) 0% to 1% by weight of methyl methacrylate;    -   (d) 55% to 70% by weight of n-butyl methacrylate;    -   (e) 5% to 20% by weight of C₁₀₋₃₀ alkyl (meth)acrylates,        preferably C₁₀₋₁₅ alkyl methacrylates, more preferably C₁₂₋₁₄        alkyl methacrylates; and    -   (f) 0% to 2% by weight of styrene monomers.

A further preferred first embodiment is directed to thepolyalkyl(meth)acrylate based comb polymers, comprising the followingmonomers:

-   -   (a) 13 to 23% by weight of an ester of (meth)acrylic acid and a        hydroxylated hydrogenated polybutadiene;    -   (b) 0.5% to 11% by weight, preferably 0.5 to 5% by weight, of        C₄₋₁₈ alkyl acrylates;    -   (c) 0.1% to 0.3% by weight of methyl methacrylate;    -   (d) 55% to 70% by weight of n-butyl methacrylate;    -   (e) 5% to 18% by weight of C₁₀₋₁₅ alkyl methacrylates,        preferably C₁₂₋₁₄ alkyl methacrylates; and    -   (f) 0.1% to 2% by weight of styrene monomers.

A further preferred first embodiment is directed to thepolyalkyl(meth)acrylate based comb polymers, comprising the followingmonomers:

-   -   (a) 13 to 14% by weight of an ester of (meth)acrylic acid and a        hydroxylated hydrogenated polybutadiene;    -   (b) 0.5% to 5% by weight of C₄₋₁₈ alkyl acrylates;    -   (c) 0.1% to 0.3% by weight of methyl methacrylate;    -   (d) 63% to 70% by weight of n-butyl methacrylate;    -   (e) 13% to 18% by weight of C₁₀₋₁₅ alkyl methacrylates,        preferably C₁₂₋₁₄ alkyl methacrylates; and    -   (f) 0.1% to 0.3% by weight of styrene monomers.

A further preferred first embodiment is directed to thepolyalkyl(meth)acrylate based comb polymers, comprising the followingmonomers:

-   -   (a) 13 to 14% by weight of an ester of (meth)acrylic acid and a        hydroxylated hydrogenated polybutadiene;    -   (b) 0.5% to 5% by weight of C₄₋₁₈ alkyl acrylates;    -   (c) 0.1% to 0.3% by weight of methyl methacrylate;    -   (d) 66% to 70% by weight of n-butyl methacrylate;    -   (e) 16% to 18% by weight of C₁₀₋₁₅ alkyl methacrylates,        preferably C₁₂₋₁₄ alkyl methacrylates; and    -   (f) 0.1% to 0.3% by weight of styrene monomers.

The content of each component (a), (b), (c), (d), (e) and (f) is basedon the total composition of the polyalkyl(meth)acrylate based combpolymer. In a particular embodiment, the proportions of components (a),(b), (c), (d), (e) and (f) add up to 100% by weight.

The weight-average molecular weight M_(w) of the polyalkyl(meth)acrylatebased comb polymers according to the present invention is preferably inthe range from 200.000 to 800.000 g/mol, and more preferably from300.000 to 600.000 g/mol.

Preferably, the polyalkyl(meth)acrylate based comb polymers according tothe present invention have a polydipersity index (PDI) M_(w)/M_(n) inthe range of 1 to 6, more preferably in the range of from 3 to 5.

M_(w) and M_(n) are determined by size exclusion chromatography (SEC)using commercially available polymethylmethacrylate standards. Thedetermination is effected by gel permeation chromatography with THF aseluent.

A comb polymer in the context of this invention comprises a firstpolymer, which is also referred to as backbone or main chain, and amultitude of further polymers which are referred to as side chains andare bonded covalently to the backbone. In the present case, the backboneof the comb polymer is formed by the interlinked unsaturated groups ofthe mentioned (meth)acrylates. The ester groups of the (meth)acrylicesters, the phenyl radicals of the styrene monomers and the substituentsof the further free-radically polymerizable comonomers form the sidechains of the comb polymer.

The term “acrylate” refers to esters of acrylic acid; the term“methacrylate” refers to esters of methacrylic acid; and the term“(meth)acrylate” refers to both, esters of acrylic acid and estersmethacrylic acid.

The C₄₋₁₈ alkyl acrylates for use in accordance with the invention areesters of acrylic acid and alcohols having 4 to 18 carbon atoms. Theterm “C₄₋₁₈ alkyl acrylates” encompasses individual acrylic esters withan alcohol of a particular length, and likewise mixtures of acrylicesters with alcohols of different lengths.

The suitable C₄₋₁₈ alkyl acrylates include, for example, butyl acrylate,pentyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, heptyl acrylate,2-tert-butylheptyl acrylate, octyl acrylate, 3-isopropylheptyl acrylate,nonyl acrylate, decyl acrylate, undecyl acrylate, 5-methylundecylacrylate, dodecyl acrylate, 2-methyldodecyl acrylate, tridecyl acrylate,5-methyltridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate,hexadecyl acrylate, 2-methylhexadecyl acrylate, heptadecyl acrylateand/or octadecyl acrylate.

Particularly preferred C₄₋₁₈ alkyl acrylates are butyl acrylate andacrylic esters of a linear C₁₆₋₁₈ alcohol mixture (C₁₆₋₁₈ alkylacrylate).

The C₁₀₋₃₀ alkyl (meth)acrylates for use in accordance with theinvention are esters of (meth)acrylic acid and straight chain orbranched alcohols having 10 to 30 carbon atoms. The term “C₁₀₋₃₀ alkylmethacrylates” encompasses individual (meth)acrylic esters with analcohol of a particular length, and likewise mixtures of (meth)acrylicesters with alcohols of different lengths.

Suitable C₁₀₋₃₀ alkyl (meth)acrylates include, for example, 2-butyloctyl(meth)acrylate, 2-hexyloctyl (meth)acrylate, decyl (meth)acrylate,2-butyldecyl (meth)acrylate, 2-hexyldecyl (meth)acrylate, 2-octyldecyl(meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate,dodecyl (meth)acrylate, 2-methyldodecyl (meth)acrylate, 2-hexyldodecyl(meth)acrylate, 2-octyldodecyl (meth)acrylate, tridecyl (meth)acrylate,5-methyltridecyl (meth)acrylate, tetradecyl (meth)acrylate,2-decyltetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl(meth)acrylate, 2-methylhexadecyl (meth)acrylate, 2-dodecylhexadecyl(meth)acrylate, heptadecyl (meth)acrylate, 5-isopropylheptadecyl(meth)acrylate, 4-tert-butyloctadecyl (meth)acrylate, 5-ethyloctadecyl(meth)acrylate, 3-isopropyloctadecyl (meth)acrylate, octadecyl(meth)acrylate, 2-decyloctadecyl (meth)acrylate, 2-tetradecyloctadecyl(meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate,cetyleicosyl (meth)acrylate, stearyleicosyl (meth)acrylate, docosyl(meth)acrylate and/or eicosyltetratriacontyl (meth)acrylate.2-decyl-tetradecyl (meth)acrylate, 2-decyloctadecyl (meth)acrylate,2-dodecyl-1-hexadecyl (meth)acrylate, 1,2-octyl-1-dodecyl(meth)acrylate, 2-tetradecylocadecyl (meth)acrylate,1,2-tetradecyl-octadecyl (meth)acrylate and 2-hexadecyl-eicosyl(meth)acrylate.

The C₁₀₋₁₅ alkyl methacrylates for use in accordance with the inventionare esters of methacrylic acid and alcohols having 10 to 15 carbonatoms. The term “C₁₀₋₁₅ alkyl methacrylates” encompasses individualmethacrylic esters with an alcohol of a particular length, and likewisemixtures of methacrylic esters with alcohols of different lengths.

The suitable C₁₀₋₁₅ alkyl methacrylates include, for example, decylmethacrylate, undecyl methacrylate, 5-methylundecyl methacrylate,dodecyl methacrylate, 2-methyldodecyl methacrylate, tridecylmethacrylate, 5-methyltridecyl methacrylate, tetradecyl methacrylateand/or pentadecyl methacrylate.

Particularly preferred C₁₀₋₁₅ alkyl methacrylates are methacrylic estersof a linear C₁₂₋₁₄ alcohol mixture (C₁₂₋₁₄ alkyl methacrylate).

The hydroxylated hydrogenated polybutadiene for use in accordance withthe invention has a number-average molar mass M_(n) of 4.000 to 6.000g/mol, preferably 4.000 to 5.000 g/mol. Because of their high molarmass, the hydroxylated hydrogenated polybutadienes can also be referredto as macroalcohols in the context of this invention.

The number-average molar mass M_(n) is determined by size exclusionchromatography using commercially available polybutadiene standards. Thedetermination is effected to DIN 55672-1 by gel permeationchromatography with THF as eluent.

Preferably, the hydroxylated hydrogenated polybutadiene has ahydrogenation level of at least 99%. An alternative measure of thehydrogenation level which can be determined on the copolymer of theinvention is the iodine number. The iodine number refers to the numberof grams of iodine which can be added onto 100 g of copolymer.Preferably, the copolymer of the invention has an iodine number of notmore than 5 g of iodine per 100 g of copolymer. The iodine number isdetermined by the Wijs method according to DIN 53241-1:1995-05.

Preferred hydroxylated hydrogenated polybutadienes can be obtainedaccording to GB 2270317.

Some hydroxylated hydrogenated polybutadienes are also commerciallyavailable. The commercially hydroxylated hydrogenated polybutadienesinclude, for example, Kraton Liquid® L-1203, a hydrogenatedpolybutadiene OH-functionalized to an extent of about 98% by weight(also called olefin copolymer OCP) having about 50% each of 1,2 repeatunits and 1,4 repeat units, of M_(n)=4200 g/mol, from Kraton PolymersGmbH (Eschborn, Germany). A further supplier of suitable alcohols basedon hydrogenated polybutadiene is Cray Valley (Paris), a daughter companyof Total (Paris), or the Sartomer Company (Exton, Pa., USA).

Preference is given to monohydroxylated hydrogenated polybutadienes.More preferably, the hydroxylated hydrogenated polybutadiene is ahydroxyethyl- or hydroxypropyl-terminated hydrogenated polybutadiene.Particular preference is given to hydroxypropyl-terminatedpolybutadienes.

These monohydroxylated hydrogenated polybutadienes can be prepared byfirst converting butadiene monomers by anionic polymerization topolybutadiene. Subsequently, by reaction of the polybutadiene monomerswith ethylene oxide or propylene oxide, a hydroxy-functionalizedpolybutadiene can be prepared. This hydroxylated polybutadiene can behydrogenated in the presence of a suitable transition metal catalyst.

The esters of (meth)acrylic acid for use in accordance with theinvention and a hydroxylated hydrogenated polybutadiene described arealso referred to as macromonomers in the context of this inventionbecause of their high molar mass.

The macromonomers for use in accordance with the invention can beprepared by transesterification of alkyl (meth)acrylates. Reaction ofthe alkyl (meth)acrylate with the hydroxylated hydrogenatedpolybutadiene forms the ester of the invention. Preference is given tousing methyl (meth)acrylate or ethyl (meth)acrylate as reactant.

This transesterification is widely known. For example, it is possiblefor this purpose to use a heterogeneous catalyst system, such as lithiumhydroxide/calcium oxide mixture (LiOH/CaO), pure lithium hydroxide(LiOH), lithium methoxide (LiOMe) or sodium methoxide (NaOMe) or ahomogeneous catalyst system such as isopropyl titanate (Ti(OiPr)₄) ordioctyltin oxide (Sn(OCt)₂O). The reaction is an equilibrium reaction.Therefore, the low molecular weight alcohol released is typicallyremoved, for example by distillation.

In addition, the macromonomers can be obtained by a directesterification proceeding, for example, from (meth)acrylic acid or(meth)acrylic anhydride, preferably under acidic catalysis byp-toluenesulfonic acid or methanesulfonic acid, or from free methacrylicacid by the DCC method (dicyclohexylcarbodiimide).

Furthermore, the present hydroxylated hydrogenated polybutadiene can beconverted to an ester by reaction with an acid chloride such as(meth)acryloyl chloride.

Preferably, in the above-detailed preparations of the esters of theinvention, polymerization inhibitors are used, for example the4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl radical and/or hydroquinonemonomethyl ether.

Some of the macromonomers for use in accordance with the invention arealso commercially available, for example Kraton Liquid® L-1253 which isproduced from Kraton Liquid® L-1203 and is a hydrogenated polybutadienemethacrylate-functionalized to an extent of about 96% by weight, havingabout 50% each of 1,2 repeat units and 1,4 repeat units, from KratonPolymers GmbH (Eschborn, Germany). Kraton® L-1253 is likewisesynthesized according to GB 2270317.

The copolymer for use in accordance with the invention can becharacterized on the basis of its molar branching level (“f-branch”).The molar branching level refers to the percentage in mol % ofmacromonomers (component (A)) used, based on the total molar amount ofall the monomers in the monomer composition. The molar amount of themacromonomers used is calculated on the basis of the number-averagemolar mass M_(n) of the macromonomers. The calculation of the branchinglevel is described in detail in WO 2007/003238 A1, especially on pages13 and 14, to which reference is made here explicitly.

The polyalkyl(meth)acrylate based comb polymers in accordance with theinvention preferably have a molar degree of branching f_(branch) of 0.1to 2 mol %, more preferably 0.3 to 1.5 mol % and most preferably 0.5 to1.1 mol %.

The molar degree of branching fbranch is calculated as described in US2010/0190671 A1 in paragraphs [0060] to [0065].

The polyalkyl(meth)acrylate based comb polymers in accordance with theinvention can be prepared by free-radical polymerization and by relatedmethods of controlled free-radical polymerization, for example ATRP(=atom transfer radical polymerization) or RAFT (=reversible additionfragmentation chain transfer).

Standard free-radical polymerization is detailed, inter alia, inUllmann's Encyclopedia of Industrial Chemistry, Sixth Edition. Ingeneral, a polymerization initiator and optionally a chain transferagent are used for this purpose.

The usable initiators include azo initiators widely known in thetechnical field, such as AIBN and 1,1-azobiscyclohexanecarbonitrile, andalso peroxy compounds such as methyl ethyl ketone peroxide,acetylacetone peroxide, dilauryl peroxide, tert-butylper-2-ethylhexanoate, ketone peroxide, tert-butyl peroctoate, methylisobutyl ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide,tert-butyl peroxybenzoate, tert-butyl peroxyisopropylcarbonate,2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate,dicumyl peroxide, 1,1-bis(tert-butylperoxy)cyclohexane,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, cumylhydroperoxide, tert-butyl hydroperoxide, bis(4-tert-butylcyclohexyl)peroxydicarbonate, mixtures of two or more of the aforementionedcompounds with one another, and mixtures of the aforementioned compoundswith unspecified compounds which can likewise form free radicals.Suitable chain transfer agents are especially oil-soluble mercaptans,for example n-dodecyl mercaptan or 2-mercaptoethanol, or else chaintransfer agents from the class of the terpenes, for example terpinolene.

The ATRP method is known per se. It is assumed that this is a “living”free-radical polymerization, but no restriction is intended by thedescription of the mechanism. In these processes, a transition metalcompound is reacted with a compound having a transferable atom group.This involves transfer of the transferable atom group to the transitionmetal compound, as a result of which the metal is oxidized. Thisreaction forms a free radical which adds onto ethylenic groups. However,the transfer of the atom group to the transition metal compound isreversible, and so the atom group is transferred back to the growingpolymer chain, which results in formation of a controlled polymerizationsystem. It is accordingly possible to control the formation of thepolymer, the molecular weight and the molecular weight distribution.

This reaction regime is described, for example, by J.-S. Wang, et al.,J. Am. Chem. Soc, vol. 117, p. 5614-5615 (1995), by Matyjaszewski,Macromolecules, vol. 28, p. 7901-7910 (1995). In addition, patentapplications WO 96/30421, WO 97/47661, WO 97/18247, WO 98/40415 and WO99/10387 disclose variants of the above-elucidated ATRP. In addition,the polymers of the invention can also be obtained via RAFT methods, forexample. This method is described in detail, for example, in WO 98/01478and WO 2004/083169.

The polymerization can be conducted under standard pressure, reducedpressure or elevated pressure. The polymerization temperature is alsouncritical. In general, however, it is in the range from −20 to 200° C.,preferably 50 to 150° C. and more preferably 80 to 130° C.

The polymerization can be conducted with or without solvent. The term“solvent” should be understood here in a broad sense. The solvent isselected according to the polarity of the monomers used, it beingpossible with preference to use 100N oil, comparatively light gas oiland/or aromatic hydrocarbons, for example toluene or xylene.

The polymers according to the present invention are characterized bytheir contribution to reduce Noack evaporation losses of lubricatingcompositions.

They are also characterized by excellent shear stability, low HTHSviscosity in the effective temperature range and by a high viscosityindex (low KV₄₀).

The polyalkyl(meth)acrylate based comb polymers according to the presentinvention show excellent PSSI (Permanent Shear Stability Index) valuesin lubricating base oils, especially in Group III base oils.

Preferably, the PSSI of the comb polymers according to the presentinvention is not more than 7, even more preferable below 3.

The present invention also relates to the use of the above-describedpolyalkyl(meth)acrylate based comb polymers for reducing Noackevaporation losses of lubricating compositions, especially of engine oilcompositions.

The present invention further relates to a method of reducing Noackevaporation losses of lubricating compositions, especially of engine oilcompositions, by applying the above-described polyalkyl(meth)acrylatebased comb polymers.

By using the polyalkyl(meth)acrylate based comb polymers according tothe present invention, the Noack evaporation losses of lubricatingcompositions can be reduced by up to 10.8%, based on a 0W20 formulation.

For a thicker formulation, e.g. 5W30, which usually contains a higheramount of VI improver, the reduction would be even higher.

The polyalkyl(meth)acrylate based comb polymers according to the presentinvention can therefore be used in all common grades of motor oilshaving the viscosity characteristics defined in the document SAE J300.

A second object of the present invention is directed to an additivecomposition, comprising:

-   -   (A) a base oil, and    -   (B) a polyalkyl(meth)acrylate based comb polymer, comprising the        following monomers:        -   (a) 10 to 25% by weight of esters of (meth)acrylic acid and            a hydroxylated hydrogenated polybutadiene; and        -   (b) 0.5% to 11% by weight, preferably 0.5 to 5% by weight,            of C₄₋₁₈ alkyl acrylates.

A preferred second object is directed to an additive composition,comprising:

-   -   (A) a base oil; and    -   (B) a polyalkyl(meth)acrylate based comb polymer, comprising the        following monomers:        -   (a) 10 to 25% by weight of an ester of (meth)acrylic acid            and a hydroxylated hydrogenated polybutadiene;        -   (b) 0.5% to 11% by weight of C₄₋₁₈ alkyl acrylates;        -   (c) 0% to 1% by weight of methyl methacrylate;        -   (d) 55% to 70% by weight of n-butyl methacrylate;        -   (e) 5% to 20% by weight of C₁₀₋₁₅ alkyl methacrylates,            preferably C₁₂₋₁₄ alkyl methacrylates; and        -   (f) 0% to 2% by weight of styrene monomers.

A further preferred second object is directed to an additivecomposition, comprising:

-   -   (A) a base oil; and    -   (B) a polyalkyl(meth)acrylate based comb polymer, comprising the        following monomers:        -   (a) 13 to 23% by weight of an ester of (meth)acrylic acid            and a hydroxylated hydrogenated polybutadiene;        -   (b) 0.5% to 11% by weight of C₄₋₁₈ alkyl acrylates;        -   (c) 0.1% to 0.3% by weight of methyl methacrylate;        -   (d) 55% to 70% by weight of n-butyl methacrylate;        -   (e) 5% to 18% by weight of C₁₀₋₁₅ alkyl methacrylates,            preferably C₁₂₋₁₄ alkyl methacrylates; and        -   (f) 0.1% to 2% by weight of styrene monomers.

A further preferred second object is directed to an additivecomposition, comprising:

-   -   (A) a base oil; and    -   (B) a polyalkyl(meth)acrylate based comb polymer, comprising the        following monomers:        -   (a) 13 to 14% by weight of an ester of (meth)acrylic acid            and a hydroxylated hydrogenated polybutadiene;        -   (b) 0.5% to 5% by weight of C₄₋₁₈ alkyl acrylates;        -   (c) 0.1% to 0.3% by weight of methyl methacrylate;        -   (d) 63% to 70% by weight of n-butyl methacrylate;        -   (e) 13% to 18% by weight of C₁₀₋₁₅ alkyl methacrylates,            preferably C₁₂₋₁₄ alkyl methacrylates; and        -   (f) 0.1% to 0.3% by weight of styrene monomers.

A further preferred second object is directed to an additivecomposition, comprising:

-   -   (A) a base oil; and    -   (B) a polyalkyl(meth)acrylate based comb polymer, comprising the        following monomers:        -   (a) 13 to 14% by weight of an ester of (meth)acrylic acid            and a hydroxylated hydrogenated polybutadiene;        -   (b) 0.5% to 5% by weight of C₄₋₁₈ alkyl acrylates;        -   (c) 0.1% to 0.3% by weight of methyl methacrylate;        -   (d) 66% to 70% by weight of n-butyl methacrylate;        -   (e) 16% to 18% by weight of C₁₀₋₁₅ alkyl methacrylates,            preferably C₁₂₋₁₄ alkyl methacrylates; and        -   (f) 0.1% to 0.3% by weight of styrene monomers.

The content of each component (a), (b), (c), (d), (e) and (f) is basedon the total composition of the polyalkyl(meth)acrylate based combpolymer.

In a particular embodiment, the proportions of components (a), (b), (c),(d), (e) and (f) add up to 100% by weight.

The additive compositions according to the present invention are furthercharacterized by a high viscosity index (VI). The VI is at least 245,preferably in the range of 245 to 350, more preferably in the range of250 to 310.

The base oil to be used in the additive composition comprises an oil oflubricating viscosity. Such oils include natural and synthetic oils, oilderived from hydrocracking, hydrogenation, and hydro-finishing,unrefined, refined, re-refined oils or mixtures thereof.

The base oil may also be defined as specified by the American PetroleumInstitute (API) (see April 2008 version of “Appendix E-API Base OilInterchangeability Guidelines for Passenger Car Motor Oils and DieselEngine Oils”, section 1.3 Sub-heading 1.3. “Base Stock Categories”).

The API currently defines five groups of lubricant base stocks (API1509, Annex E - API Base Oil Interchangeability Guidelines for PassengerCar Motor Oils and Diesel Engine Oils, September 2011). Groups I, II andIII are mineral oils which are classified by the amount of saturates andsulphur they contain and by their viscosity indices; Group IV arepolyalphaolefins; and Group V are all others, including e.g. ester oils.Ester oils which can be used in accordance with the present inventionare preferably selected from the group consisting of Plastomoll DNA,DIOS and mixtures thereof; DIOS being even more preferred. The tablebelow illustrates these API classifications.

Group Saturates Sulphur content Viscosity Index (VI) I <90% >0.03%80-120 II at least 90% not more than 0.03% 80-120 III at least 90% notmore than 0.03% at least 120 IV All polyalphaolefins (PAOs) V All othersnot included in Groups I, II, III or IV (e.g. ester oils)

The kinematic viscosity at 100° C. (KVioo) of appropriate apolar baseoils used to prepare an additive composition or lubricating compositionin accordance with the present invention is preferably in the range of 3mm²/s to 10 mm²/s, more preferably in the range of 4 mm²/s to 8 mm²/s,according to ASTM D445.

Further base oils which can be used in accordance with the presentinvention are Group II-III Fischer-Tropsch derived base oils.

Fischer-Tropsch derived base oils are known in the art. By the term“Fischer-Tropsch derived” is meant that a base oil is, or is derivedfrom, a synthesis product of a Fischer-Tropsch process. AFischer-Tropsch derived base oil may also be referred to as a GTL(Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oilsthat may be conveniently used as the base oil in the lubricatingcomposition of the present invention are those as for example disclosedin EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029029, WO 01/18156, WO 01/57166 and WO 2013/189951.

Especially for engine oil formulations are used base oils of API GroupIII.

The additive composition of the present invention comprises preferably60% to 80% by weight of base oil (component (A)), preferably 70% to 75%by weight, based on the total weight of the additive composition.

Further preferred is an additive composition, comprising as component(A):

-   -   (A1) 54 to 80% by weight, preferably 64 to 75% by weight, of a        base oil selected from the group consisting of API Group I oils,        Group II oils, Group III oils, Group IV oils and mixture        thereof, and    -   (A2) 0 to 6% by weight of API Group V oils, preferably        dioctylsebacate (DIOS), based on the total weight of the        additive composition.

Even further preferred is an additive composition, comprising ascomponent (A):

-   -   (A1) 54 to 76% by weight, preferably 64 to 71% by weight, of a        base oil selected from the group consisting of API Group I oils,        Group II oils, Group III oils, Group IV oils and mixture        thereof, and    -   (A2) 4 to 6% by weight, of API Group V oils, preferably        dioctylsebacate (DIOS), based on the total weight of the        additive composition.

The concentration of the polyalkyl(meth)acrylate based comb polymer(component (B)) in the additive composition is preferably in the rangefrom 20% to 40% by weight, more preferably in the range of 25% to 30% byweight, based on the total weight of the additive composition.

Further preferred contents of components (A) and (B) in the additivecompositions according to the present invention are as detailed in thefollowing table:

Additive Component (A) Component (B) Composition [% by weight] [% byweight] (1) 60 to 80 20 to 40 (2) (A1) 54 to 80 20 to 40 (A2) 0 to 6 (3)(A1) 54 to 76 20 to 40 (A2) 4 to 6 (4) 70 to 75 25 to 30 (5) (A1) 64 to75 25 to 30 (A2) 0 to 6 (6) (A1) 64 to 71 25 to 30 (A2) 4 to 6

The content of each component (A) and (B) is based on the total weightof the additive composition.

In a particular embodiment, the proportions of components (A) and (B)add up to 100% by weight.

The present invention also relates to the above-described additivecomposition, which is characterized by its reduced Noack evaporationloss.

The present invention therefore further relates to the additivecomposition described above, which preferably has a Noack evaporationloss in the range of 15 to 20%, determined at 250° C. for 1 hour to CECL-40B.

The present invention further relates to the use of the above-describedadditive compositions as viscosity index (VI) improvers which, at thesame time, reduce the Noack evaporation losses of lubricating oilcompositions.

By using the additive compositions according to the present invention,Noack evaporation losses can be reduced by up to 48%, determined at 250°C. for 1 hour to CEC L-40B.

The present invention further relates to a method of reducing Noackevaporation losses of lubricating oil compositions, especially of engineoil compositions, by applying the above-described additive compositions.

The additive compositions are further defined by excellent shearstability (low PSSI values) and low KV4o values.

A third object of the present invention is directed to a lubricating oilcomposition, comprising:

-   -   (A) 75 to 99.5% by weight of a base oil;    -   (B) 0.5 to 10% by weight of a polyalkyl(meth)acrylate based comb        polymer, comprising the following monomers:        -   (a) 10 to 25% by weight of esters of (meth)acrylic acid and            a hydroxylated hydrogenated polybutadiene;        -   (b) 0.5% to 11% by weight, preferably 0.5 to 5% by weight,            of C₄₋₁₈ alkyl acrylates; and    -   (C) 0 to 15% by weight of one or more further additives.

A preferred third object of the present invention is directed to alubricating oil composition, comprising:

-   -   (A) 75 to 99.5% by weight of a base oil;    -   (B) 0.5 to 10% by weight of a polyalkyl(meth)acrylate based comb        polymer, comprising the following monomers:        -   (a) 10 to 25% by weight of an ester of (meth)acrylic acid            and a hydroxylated hydrogenated polybutadiene;        -   (b) 0.5% to 11% by weight of C₄₋₁₈ alkyl acrylates;        -   (c) 0% to 1% by weight of methyl methacrylate;        -   (d) 55% to 70% by weight of n-butyl methacrylate;        -   (e) 5% to 20% by weight of C₁₀₋₁₅ alkyl methacrylates,            preferably C₁₂₋₁₄ alkyl methacrylates;        -   (f) 0% to 2% by weight of styrene monomers; and    -   (C) 0 to 15% by weight of one or more further additives.

A further preferred third object of the present invention is directed toa lubricating oil composition, comprising:

-   -   (A) 75 to 99.5% by weight of a base oil;    -   (B) 0.5 to 10% by weight of a polyalkyl(meth)acrylate based comb        polymer, comprising the following monomers:        -   (a) 13 to 23% by weight of an ester of (meth)acrylic acid            and a hydroxylated hydrogenated polybutadiene;        -   (b) 0.5% to 11% by weight of C₄₋₁₈ alkyl acrylates;        -   (c) 0.1% to 0.3% by weight of methyl methacrylate;        -   (d) 55% to 70% by weight of n-butyl methacrylate;        -   (e) 5% to 18% by weight of C₁₀₋₁₅ alkyl methacrylates,            preferably C₁₂₋₁₄ alkyl methacrylates;        -   (f) 0.1% to 2% by weight of styrene monomers;    -   (C) 0 to 15% by weight of one or more further additives.

A further preferred third object of the present invention is directed toa lubricating oil composition, comprising:

-   -   (A) 75 to 99.5% by weight of a base oil;    -   (B) 0.5 to 10% by weight of a polyalkyl(meth)acrylate based comb        polymer, comprising the following monomers:        -   (a) 13 to 14% by weight of an ester of (meth)acrylic acid            and a hydroxylated hydrogenated polybutadiene;        -   (b) 0.5% to 5% by weight of C₄₋₁₈ alkyl acrylates;        -   (c) 0.1% to 0.3% by weight of methyl methacrylate;        -   (d) 63% to 70% by weight of n-butyl methacrylate;        -   (e) 13% to 18% by weight of C₁₀₋₁₅ alkyl methacrylates,            preferably C₁₂₋₁₄ alkyl methacrylates;        -   (f) 0.1% to 0.3% by weight of styrene monomers, and    -   (C) 0 to 15% by weight of one or more further additives.

A further preferred third object of the present invention is directed toa lubricating oil composition, comprising:

-   -   (A) 75 to 99.5% by weight of a base oil;    -   (B) 0.5 to 10% by weight of a polyalkyl(meth)acrylate based comb        polymer, comprising the following monomers:        -   (a) 13 to 14% by weight of an ester of (meth)acrylic acid            and a hydroxylated hydrogenated polybutadiene;        -   (b) 0.5% to 5% by weight of C₄₋₁₈ alkyl acrylates;        -   (c) 0.1% to 0.3% by weight of methyl methacrylate;        -   (d) 66% to 70% by weight of n-butyl methacrylate;        -   (e) 16% to 18% by weight of C₁₀₋₁₅ alkyl methacrylates,            preferably C₁₂₋₁₄ alkyl methacrylates;        -   (f) 0.1% to 0.3% by weight of styrene monomers; and    -   (C) 0 to 15% by weight of one or more further additives.

The content of each component (a), (b), (c), (d), (e) and (f) is basedon the total composition of the polyalkyl(meth)acrylate based combpolymer.

In a particular embodiment, the proportions of components (a), (b), (c),(d), (e) and (f) add up to 100% by weight.

The content of each component (A), (B) and (C) is based on the totalcomposition of the lubricating oil composition.

The lubricating oil compositions according to the present invention arecharacterized by their low Noack evaporation losses.

The present invention therefore further relates to the lubricating oilcomposition described above, which preferably has a Noack evaporationloss of 12.8 to 15.2%, determined at 250° C. for 1 hour to CEC L-40B.

The lubricating oil compositions according to the present invention arefurther characterized by their low HTHS₁₀₀ and HTHS₈₀ values, determinedto CEC L-036, and their low KV₄₀ values, determined to ASTM D445.

Especially, when formulated to a given HTHS₁₅₀ target of 2.6 mPas for a0W20 formulation according to SAE J300 the lubricating oil formulationsof the present invention show HTHS₁₀₀ values in the range of 4.0 to 5.0mPas and KV₄₀ values in the range of 23 to 25 mm²/s.

The present invention also relates to the above-described lubricatingoil composition, which is characterized by its reduced CCS(Cold-Cranking Simulator) apparent viscosity at −35° C. to ASTM D 5293.

The lubricating oil composition of the present invention comprisespreferably 80 to 99.5% by weight of a base oil (component (A)), based onthe total weight of the lubricating oil composition.

Further preferred is a lubricating oil composition, comprising ascomponent (A):

-   -   (A1) 74.25 to 99.45% by weight of a base oil selected from the        group consisting of API Group I oils, Group II oils, Group III        oils, Group IV oils and mixture thereof, and    -   (A2) 0.05 to 0.75% by weight of API Group V oils, preferably        dioctylsebacate, based on the total weight of the lubricating        oil composition.

The concentration of the polyalkyl(meth)acrylate polymer (component (B))in the lubricating oil composition is preferably in the range of 0.5 to5% by weight, more preferably in the range of 2 to 4% by weight, basedon the total weight of the lubricating oil composition.

Further preferred contents of components (A), (B) and (C) in thelubricating oil compositions according to the present invention are asdetailed in the following table:

Lubricating Oil Component (A) Component (B) Component (C) Composition [%by weight] [% by weight] [% by weight] (1) 75 to 99.5 0.5 to 10 0 to 15(1a) (A1) 74.25 to 99.45 0.5 to 10 0 to 15 (A2) 0.05 to 0.75 (2) 80 to99.5 0.5 to 5 0 to 15 (2a) (A1) 79.25 to 99.45 0.5 to 5 0 to 15 (A2)0.05 to 0.75 (3) 81 to 98 2 to 4 0 to 15 (3a) (A1) 80.25 to 97.95 2 to 40 to 15 (A2) 0.05 to 0.75 (4) 80 to 96.5 0.5 to 10 3 to 10 (4a) (A1)79.25 to 96.45 0.5 to 10 3 to 10 (A2) 0.05 to 0.75 (5) 85 to 96.5 0.5 to5 3 to 10 (5a) (A1) 84.25 to 96.45 0.5 to 5 3 to 10 (A2) 0.05 to 0.75(6) 86 to 95 2 to 4 3 to 10 (6a) (A1) 85.25 to 94.95 2 to 4 3 to 10 (A2)0.05 to 0.75

In a particular embodiment, the proportions of components (A), (B) and(C) add up to 100% by weight.

The lubricating oil composition according to the invention may alsocontain, as component (C), further additives selected from the groupconsisting of conventional VI improvers, dispersants, defoamers,detergents, antioxidants, pour point depressants, antiwear additives,extreme pressure additives, friction modifiers, anticorrosion additives,dyes and mixtures thereof.

Conventional VI improvers include hydrogenated styrene-diene copolymers(HSDs, U.S. Pat. Nos. 4,116,917, 3,772,196 and 4,788,316), especiallybased on butadiene and isoprene, and also olefin copolymers (OCPs, K.Marsden: “Literature Review of OCP Viscosity Modifiers”, LubricationScience 1 (1988), 265), especially of the poly(ethylene-co-propylene)type, which may often also be present in N/O-functional form withdispersing action, or PAMAs, which are usually present in N-functionalform with advantageous additive properties (boosters) as dispersants,wear protection additives and/or friction modifiers (DE 1 520 696 toRohm and Haas, WO 2006/007934 to RohMax Additives).

Compilations of VI improvers and pour point improvers for lubricantoils, especially motor oils, are detailed, for example, in T. Mang, W.Dresel (eds.): “Lubricants and Lubrication”, Wiley-VCH, Weinheim 2001:R. M. Mortier, S. T. Orszulik (eds.): “Chemistry and Technology ofLubricants”, Blackie Academic & Professional, London 1992; or J. Bartz:“Additive fur Schmierstoffe”, Expert-Verlag, Renningen-Malmsheim 1994.

Appropriate dispersants include poly(isobutylene) derivatives, forexample poly(isobutylene)succinimides (PIBSIs), including boratedPIBSIs; and ethylene-propylene oligomers having N/O functionalities.

Dispersants (including borated dispersants) are preferably used in anamount of 0 to 5% by weight, based on the total amount of thelubricating oil composition.

Suitable defoamers are silicone oils, fluorosilicone oils, fluoroalkylethers, etc.

The defoaming agent is preferably used in an amount of 0.005 to 0.1% byweight, based on the total amount of the lubricating oil composition.

The preferred detergents include metal-containing compounds, for examplephenoxides; salicylates; thiophosphonates, especiallythiopyrophosphonates, thiophosphonates and phosphonates; sulfonates andcarbonates. As metal, these compounds may contain especially calcium,magnesium and barium. These compounds may preferably be used in neutralor overbased form.

Detergents are preferably used in an amount of 0.2 to 1% by weight,based on the total amount of the lubricating oil composition.

The suitable antioxidants include, for example, phenol-basedantioxidants and amine-based antioxidants.

Phenol-based antioxidants include, for example,octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate;4,4′-methylenebis(2,6-di-tert-butylphenol);4,4′-bis(2,6-di-t-butylphenol); 4,4′-b is(2-methyl-6-t-butylphenol);2,2′-methylenebis(4-ethyl-6-t-butylphenol);2,2′-methylenebis(4-methyl-6-t-butyl phenol);4,4′-butylidenebis(3-methyl-6-t-butylphenol);4,4′-isopropylidenebis(2,6-di-t-butylphenol);2,2′-methylenebis(4-methyl-6-nonylphenol);2,2′-isobutylidenebis(4,6-dimethylphenol);2,2′-methylenebis(4-methyl-6-cyclohexylphenol);2,6-di-t-butyl-4-methylphenol; 2,6-di-t-butyl-4-ethyl-phenol;2,4-dimethyl-6-t-butylphenol; 2,6-di-t-amyl-p-cresol;2,6-di-t-butyl-4-(N,N′-dimethylaminomethylphenol);4,4′thiobis(2-methyl-6-t-butylphenol);4,4′-thiobis(3-methyl-6-t-butylphenol);2,2′-thiobis(4-methyl-6-t-butylphenol);bis(3-methyl-4-hydroxy-5-t-butylbenzyl) sulfide;bis(3,5-di-t-butyl-4-hydroxybenzyl) sulfide;n-octyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate;n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate;2,2′-thio[diethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],etc. Of those, especially preferred are bis-phenol-based antioxidantsand ester group containing phenol-based antioxidants. The amine-basedantioxidants include, for example, monoalkyldiphenylamines such asmonooctyldiphenylamine, monononyldiphenylamine, etc.;dialkyldiphenylamines such as 4,4′-dibutyldiphenylamine,4,4′-dipentyldiphenylamine, 4,4′-dihexyldiphenylamine,4,4′-diheptyldiphenylamine, 4,4′-dioctyldiphenylamine,4,4′-dinonyldiphenylamine, etc.; polyalkyldiphenylamines such astetrabutyldiphenylamine, tetrahexyldiphenylamine,tetraoctyldiphenylamine, tetranonyldiphenylamine, etc.; naphthylamines,concretely alpha-naphthylamine, phenyl-alpha-naphthylamine and furtheralkyl-substituted phenyl-alpha-naphthylamines such asbutylphenyl-alpha-naphthylamine, pentylphenyl-alpha-naphthylamine,hexylphenyl-alpha-naphthylamine, heptylphenyl-alpha-naphthylamine,octylphenyl-alpha-naphthylamine, nonylphenyl-alpha-naphthylamine, etc.Of those, diphenylamines are preferred to naphthylamines, from theviewpoint of the antioxidation effect thereof.

Suitable antioxidants may further be selected from the group consistingof compounds containing sulfur and phosphorus, for example metaldithiophosphates, for example zinc dithiophosphates (ZnDTPs), “OOStriesters”=reaction products of dithiophosphoric acid with activateddouble bonds from olefins, cyclopentadiene, norbornadiene, α-pinene,polybutene, acrylic esters, maleic esters (ashless on combustion);organosulfur compounds, for example dialkyl sulfides, diaryl sulfides,polysulfides, modified thiols, thiophene derivatives, xanthates,thioglycols, thioaldehydes, sulfur-containing carboxylic acids;heterocyclic sulfur/nitrogen compounds, especiallydialkyldimercaptothiadiazoles, 2-mercaptobenzimidazoles; zincbis(dialkyldithiocarbamate) and methylene bis(dialkyldithiocarbamate);organophosphorus compounds, for example triaryl and trialkyl phosphites;organocopper compounds and overbased calcium- and magnesium-basedphenoxides and salicylates.

Antioxidants are used in an amount of 0 to 15% by weight, preferably 0.1to 10% by weight, more preferably 0.5 to 5% by weight, based on thetotal amount of the lubricating oil composition.

The pour-point depressants include ethylene-vinyl acetate copolymers,chlorinated paraffin-naphthalene condensates, chlorinatedparaffin-phenol condensates, polymethacrylates, polyalkylstyrenes, etc.Preferred are polymethacrylates having a mass-average molecular weightof from 5.000 to 50.000 g/mol.

The amount of the pour point depressant is preferably from 0.1 to 5% byweight, based on the total amount of the lubricating oil composition.

The preferred antiwear and extreme pressure additives includesulfur-containing compounds such as zinc dithiophosphate, zincdi-C₃₋₁₂-alkyldithiophosphates (ZnDTPs), zinc phosphate, zincdithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate,disulfides, sulfurized olefins, sulfurized oils and fats, sulfurizedesters, thiocarbonates, thiocarbamates, polysulfides, etc.;phosphorus-containing compounds such as phosphites, phosphates, forexample trialkyl phosphates, triaryl phosphates, e.g. tricresylphosphate, amine-neutralized mono- and dialkyl phosphates, ethoxylatedmono- and dialkyl phosphates,phosphonates, phosphines, amine salts ormetal salts of those compounds, etc.; sulfur and phosphorus-containinganti-wear agents such as thiophosphites, thiophosphates,thiophosphonates, amine salts or metal salts of those compounds, etc.

The antiwear agent may be present in an amount of 0 to 3% by weight,preferably 0.1 to 1.5% by weight, more preferably 0.5 to 0.9% by weight,based on the total amount of the lubricating oil composition.

Friction modifiers used may include mechanically active compounds, forexample molybdenum disulfide, graphite (including fluorinated graphite),poly(trifluoroethylene), polyamide, polyimide; compounds that formadsorption layers, for example long-chain carboxylic acids, fatty acidesters, ethers, alcohols, amines, amides, imides; compounds which formlayers through tribochemical reactions, for example saturated fattyacids, phosphoric acid and thiophosphoric esters, xanthogenates,sulfurized fatty acids; compounds that form polymer-like layers, forexample ethoxylated dicarboxylic partial esters, dialkyl phthalates,methacrylates, unsaturated fatty acids, sulfurized olefins ororganometallic compounds, for example molybdenum compounds (molybdenumdithiophosphates and molybdenum dithiocarbamates MoDTCs) andcombinations thereof with ZnDTPs, copper-containing organic compounds.

Friction modifiers may be used in an amount of 0 to 6% by weight,preferably 0.05 to 4% by weight, more preferably 0.1 to 2% by weight,based on the total amount of the lubricating oil composition.

Some of the compounds listed above may fulfil multiple functions. ZnDTP,for example, is primarily an antiwear additive and extreme pressureadditive, but also has the character of an antioxidant and corrosioninhibitor (here: metal passivator/deactivator).

The above-detailed additives are described in detail, inter alia, in T.Mang, W. Dresel (eds.): “Lubricants and Lubrication”, Wiley-VCH,Weinheim 2001; R. M. Mortier, S. T. Orszulik (eds.): “Chemistry andTechnology of Lubricants”.

Preferably, the total concentration of the one or more additives (C) is0.05% to 15% by weight, more preferably 3% to 10% by weight, based onthe total weight of the lubricating oil composition.

The invention has been illustrated by the following non-limitingexamples.

EXPERIMENTAL PART

Abbreviations

-   -   AA alkyl acrylate    -   C₄ AA C₄-alkyl acrylate=n-butyl acrylate    -   C_(16/18) AA C_(16/18)-alkyl acrylate    -   AMA alkyl methacrylate    -   C₁ AMA methacrylate=methyl methacrylate (MMA)    -   C₄ AMA C₄-alkyl methacrylate=n-butyl methacrylate    -   C₁₂₋₁₅ AMA C₁₂₋₁₅-alkyl methacrylate    -   DDM dodecanethiol    -   DIOS Dioctylsebacate (CAS: 122-62-3), Group V base oil from        Sterinerie Debois with a KV₁₀₀ of 3.2 cSt    -   GTL 3 Shell Risella® X 415, Group V base oil from Shell, based        on Gas-to-Liquid Technology, with a KV₁₀₀ of 2.7 cSt    -   GTL 4 Shell Risella® X 420, Group V base oil from Shell, based        on Gas-to-Liquid Technology, with a KV₁₀₀ of 4.1 cSt    -   Gr III Oil Group III base oil mixture (NB 3043 and NB 3080 from        Neste) with a KV₁₀₀ of 4.9 cSt    -   HTHS₈₀ high-temperature high-shear viscosity @80° C., measured        according to CEC L-036    -   HTHS₁₀₀ high-temperature high-shear viscosity @100° C., measured        according to CEC L-036    -   HTHS₁₅₀ high-temperature high-shear viscosity @150° C., measured        according to CEC L-036    -   Hydroseal G232H mineral oil of petroleum origin    -   KV kinematic viscosity measured according to ASTM D445    -   KV₄₀ kinematic viscosity @40° C., measured according to ISO 3104    -   KV₁₀₀ kinematic viscosity @100° C., measured according to ISO        3104    -   LMA lauryl methacrylate, 73% C12, 27% C14, all linear    -   M_(n) number-average molecular weight    -   M_(w) weight-average molecular weight    -   NB 3020 Nexbase® 3020, Group III base oil from Neste with a        KV₁₀₀ of 2.2 cSt    -   NB 3043 Nexbase® 3043, Group III base oil from Neste with a        KV₁₀₀ of 4.3 cSt    -   OLOA 55501 DI Package for PCMO commercially available from        Oronite    -   PCMO Passenger car motor oils    -   PDI Polydispersity index    -   SMA stearyl methacrylate, 33% C16, 67% C18, all linear    -   VI viscosity index, measured according to ISO 2909    -   Yubase 3 Group III base oil from SK Lubricants with a KV₁₀₀ of        3.0 cSt    -   Yubase 4 Group III base oil from SK Lubricants with a KV₁₀₀ of        4.2 cSt

Test Methods

The comb polymers according to the present invention and the comparativeexamples were characterized with respect to their molecular weight andPDI.

Molecular weights were determined by size exclusion chromatography (SEC)using commercially available polymethylmethacrylate (PMMA) standards.The determination is effected by gel permeation chromatography with THFas eluent (flow rate: 1 mL/min; injected volume: 100 μl).

The additive compositions including the comb polymers according to thepresent invention and comparative examples were characterized withrespect to their viscosity index (VI) to ASTM D 2270, kinematicviscosity at 40° C. (KV₄₀) and 100° C. (KV₁₀₀) to ASTM D445 and withrespect to their shear stability.

To show the shear stability of the additive compositions, the PSSI(Permanent Shear Stability Index) was calculated according to ASTM D6022-01 (Standard Practice for Calculation of Permanent Shear StabilityIndex) based on data measured according to ASTM D 2603-B (Standard TestMethod for Sonic Shear Stability of Polymer-Containing Oils).

The lubricating oil compositions including the comb polymers accordingto the present invention and comparative examples were characterizedwith respect to kinematic viscosity at 40° C. (KV₄₀) and 100° C. (KV₁₀₀)to ASTM D445, the viscosity index (VI) to ASTM D 2270, high-temperaturehigh-shear viscosity at 80° C., 100° C. and 150° C. to CEC L-036, Noackevaporation loss at 250° C. for 1 hour to CEC L-40B and CCS(Cold-Cranking Simulator) apparent viscosity at −35° C. to ASTM D 5293.

Synthesis of a Hydroxylated Hydrogenated Polybutadiene

The macroalcohol prepared was a hydroxypropyl-terminated hydrogenatedpolybutadiene having a mean molar mass M_(n)=4750 g/mol.

The macroalcohol was synthesized by an anionic polymerization of1,3-butadiene with butyllithium at 20-45° C. On attainment of thedesired degree of polymerization, the reaction was stopped by addingpropylene oxide and lithium was removed by precipitation with methanol.Subsequently, the polymer was hydrogenated under a hydrogen atmospherein the presence of a noble metal catalyst at up to 140° C. and pressure200 bar. After the hydrogenation had ended, the noble metal catalyst wasremoved and organic solvent was drawn off under reduced pressure.Finally, the base oil NB 3020 was used for dilution to a polymer contentof 70% by weight.

The vinyl content of the macroalcohol was 61%, the hydrogenationlevel >99% and the OH functionality >98%. These values were determinedby H-NMR (nuclear resonance spectroscopy).

Synthesis of Macromonomer (MM)

In a 2 L stirred apparatus equipped with saber stirrer, air inlet tube,thermocouple with controller, heating mantle, column having a randompacking of 3 mm wire spirals, vapor divider, top thermometer, refluxcondenser and substrate cooler, 1000 g of the above-describedmacroalcohol are dissolved in 450 g of methyl methacrylate (MMA) bystirring at 60° C. Added to the solution are 20 ppm of2,2,6,6-tetramethylpiperidin-1-oxyl radical and 200 ppm of hydroquinonemonomethyl ether. After heating to MMA reflux (bottom temperature about110° C.) while passing air through for stabilization, about 20 g of MMAare distilled off for azeotropic drying. After cooling to 95° C., 0.30 gof LiOCH₃ is added and the mixture is heated back to reflux. After thereaction time of about 1 hour, the top temperature has fallen to ˜64° C.because of methanol formation. The methanol/MMA azeotrope formed isdistilled off constantly until a constant top temperature of about 100°C. is established again. At this temperature, the mixture is left toreact for a further hour. For further workup, the bulk of MMA is drawnoff under reduced pressure. Insoluble catalyst residues are removed bypressure filtration (Seitz T1000 depth filter). The content of NB 3020“entrained” into the copolymer syntheses described further down wastaken into account accordingly.

Synthesis of Comb Polymers

Process P1.1:

An apparatus with 4-neck flask and precision glass saber stirrer isinitially charged with a 87.5 g mixture of low molecular weight monomersand macromonomer whose composition is shown in Table 1, and with 58.3 gof an oil mixture of Hydroseal G232H/NB3020/NB3043=65.56:15.36:19.09.After heating to 90° C. under nitrogen, 0.2 g oftert-butylperoxy-2-ethyl-hexanoate is added and the temperature ismaintained. Another 245.8 g of the monomer-oil mixture and 0.2 gtert-butylperoxy-2-ethyl-hexanoate is added within 3 hours. Then thereaction is maintained at 90° C. for another 2 h. Subsequently, thereaction mixture is diluted to 40% solids with NB3043 and 0.2%tert-butylperoxy-2-ethyl-hexanoate within 3 hours. Then the reaction ismaintained at 90° C. for another 2 h and after this another 0.2%tert-butylperoxy-2-ethyl-hexanoate is added and the mixture is stirredat 90° C. overnight. The next day, the mixture is diluted to 25% solidswith NB3043. 700 g of a 25% solution of comb polymers in mineral oil areobtained. The monomer components will add up to 100%. The amounts ofinitiator and dilution oil are given relative to the total amount ofmonomers.

Process P1.2:

Polymers were prepared by radical polymerization in oil as described inthe general synthesis procedure of process P1.1 above with amodification in the oil mixture. Instead of HydrosealG232H/NB3020/NB3043, an oil mixture of DIOS/NB3020/NB3043 =20:6:74 wasused in the beginning of the reaction. The polymerization was conductedat 95° C.

Process P2:

An apparatus with 4-neck flask and precision glass saber stirrer isinitially charged with a 87.5 g mixture of low molecular weight monomersand macromonomer whose composition is shown in Table 1, and with 41.9 gof an oil mixture of DIOS/NB3020/NB3043=41.7:20.6:37.7 (Examples 2-10)or DIOS/NB3020/NB3043=41.8:13.4:44.8 (Examples 11-16). After heating to95° C. under nitrogen, 0.2 g of tert-butylperoxy-2-ethyl-hexanoate isadded and the temperature is maintained. Another 87.5 g mixture of lowmolecular weight monomers and macromonomer and 0.2 gtert-butylperoxy-2-ethyl-hexanoate diluted with 283.1 g of NB3043 isadded within 3 hours. Then the reaction is maintained at 95° C. andafter one hour and after another 3 hours 0.35 gtert-butylperoxy-2-ethyl-hexanoate is added and the mixture is stirredat 95° C. overnight. The next day, the mixture is diluted to 25% solidswith NB3043. 700 g of a 25% solution of comb polymers in mineral oil areobtained.

Table 1 shows the reaction mixtures used to prepare working examples andcomparative examples.

The monomer components will add up to 100%. The amount of initiator isgiven relative to the total amount of monomers. The remaining amount(about 75%) is dilution oil as described above in the generalproceedings used to prepare the polymers.

TABLE 1 Reaction mixtures used to prepare working examples andcomparative examples Monomers (25% of reaction mixture) C12-15 C16/18 C4C1 C4 Process MM AMA AA AA AMA AMA Styrene Initiator type/oil Ex # [%][%] [%] [%] [%] [%] [%] [%] mixture  1*⁾ 24.0 10.12 — — 0.2 64.4 1.280.2 P1.1  2*⁾ 23.0 10.27 — — 0.2 65.25 1.28 0.2 P2  3 23.0 7.77 2.5 —0.2 65.25 1.28 0.2 P2  4 23.0 5.27 5.0 — 0.2 65.25 1.28 0.2 P2  5 23.010.27 5.0 — 0.2 65.25 1.28 0.2 P2  6 23.0 5.27 10.0 — 0.2 65.25 1.28 0.2P2  7 23.0 10.27 — 2.50 0.2 62.75 1.28 0.2 P2  8 23.0 10.27 — 5.0 0.260.25 1.28 0.2 P2  9 23.0 10.27 — 10.0 0.2 55.25 1.28 0.2 P2 10 23.08.37 1.9 1.9 0.2 63.35 1.28 0.2 P2 11 15.0 17.1 1.9 1.9 0.2 63.7 0.2 0.2P2 12*⁾ 15.0 17.1 — — 0.2 67.5 0.2 0.2 P2 13 15.0 17.1 — 2.50 0.2 65.00.2 0.2 P2 14 15.0 17.1 — 5.0 0.2 62.5 0.2 0.2 P2 15 15.0 17.1 — 0.5 0.267 0.2 0.2 P2 16 15.0 17.1 — 1 0.2 66.5 0.2 0.2 P2 17 14.0 13.3 1.9 1.90.2 68.5 0.2 0.2 P1.2 18 15.0 13.1 1.9 1.9 0.2 67.7 0.2 0.2 P1.2 19*⁾23.0 10.27 — 15.0 0.2 50.25 1.28 0.2 P2 20*⁾ 23.0 10.27 — 25.0 0.2 40.251.28 0.2 P2 21 15.0 17.1 — 10.0 0.2 57.5 0.2 0.2 P2 22*⁾ 15.0 17.1 —15.0 0.2 52.5 0.2 0.2 P2 23*⁾ 15.0 17.1 — 25.0 0.2 42.5 0.2 0.2 P2 24*⁾23.0 — 15.27 — 0.2 60.25 1.28 0.2 P2 *⁾comparative example

Examples 1, 2 and 12 are comparative examples and do not comprise anyalkyl acrylates. Examples 3 to 11 and 13 to 18 are in accordance withthe present invention and comprise alkyl acrylates within the definedranges.

The net compositions of the resulting comb polymers as well as theircharacteristic weight-average molecular weights M_(w) and theirpolydispersity indices (PDI) are given in the following Table 2. Table 2further shows the macromonomer conversion rate MM_(conv), and the molardegree of branching f_(branch) of the resulting comb polymers.

TABLE 2 Net compositions of the comb polymers prepared according to thepresent invention. Monomers in net composition C12-15 C16/18 C4 C1 C4GPC results MM_(conv.) MM AMA AA AA AMA AMA Styrene M_(w) Example # [%]f_(branch) [%] [%] [%] [%] [%] [%] [%] [g/mol] PDI Example 1*⁾ 92 0.9622.51 10.32 — — 0.20 65.66 1.31 549.000 4.26 Example 2*⁾ 88 0.87 20.8110.56 — — 0.21 67.10 1.32 424.000 3.9 Example 3 90 0.91 21.19 7.95 2.56— 0.20 66.79 1.31 325.000 3.4 Example 4 91 0.93 21.37 5.38 5.11 — 0.2066.63 1.31 331.000 3.4 Example 5 90 0.95 21.19 10.51 5.12 — 0.20 61.671.31 492.000 4.3 Example 6 93 1.03 21.74 5.36 10.16  — 0.20 61.24 1.30501.000 4.5 Example 7 89 0.91 21.00 10.54 — 2.56 0.20 64.38 1.31 530.0004.9 Example 8 92 0.92 21.56 10.46 — 5.09 0.20 61.38 1.30 464.000 4.5Example 9 95 1.09 22.10 10.39 — 10.12  0.20 55.89 1.29 304.000 5.1Example 10 90 0.93 21.19 8.57 1.94 1.94 0.20 64.84 1.31 374.000 3.5Example 11 91 0.58 13.84 17.33 1.93 1.93 0.20 64.57 0.20 401.000 4.6Example 12*⁾ 89 0.54 13.57 17.39 — — 0.20 68.63 0.20 253.000 3.3 Example13 89 0.56 13.57 17.39 — 2.54 0.20 66.09 0.20 417.000 3.9 Example 14 910.59 13.84 17.33 — 5.07 0.20 63.36 0.20 404.000 4.2 Example 15 89 0.5513.57 17.39 — 0.51 0.20 68.12 0.20 497.000 4.6 Example 16 89 0.55 13.5717.39 — 1.02 0.20 67.62 0.20 419.000 4.3 Example 17 93 0.52 13.15 13.431.92 1.92 0.20 69.18 0.20 482.000 3.59 Example 18 92 0.57 13.97 13.261.92 1.92 0.20 68.52 0.20 560.000 4.91 Example 19*⁾ 97 1.19 22.47 10.34— 15.10  0.20 50.60 1.29 201000 3.84 Example 20*⁾ 97 1.44 22.47 10.34 —25.17  0.20 40.53 1.29 145000 3.67 Example 21 96 0.67 14.49 17.20 —10.06  0.20 57.85 0.20 231000 3.74 Example 22*⁾ 96 0.72 14.49 17.20 —15.09  0.20 52.82 0.20 222000 3.55 Example 23*⁾ 98 0.88 14.74 17.15 —25.08  0.20 42.63 0.20 196000 3.21 Example 24*⁾ 95 1.09 22.10 — 15.45  —0.20 60.95 1.29 251000 3.23 *⁾comparative example

Examples 3 to 7 and 11 to 18 and 21 are inventive examples and comprisethe alkyl acrylates in amounts as specified in the present invention.

Examples 1, 2 and 12 are comparative examples and do not comprise anyalkyl acrylates. Examples 19, 20 and 22-24 are comparative examples withhigher amounts of alkyl acrylates which are outside the claimed ranges.

Evaluation of the VI Improver Candidates

To demonstrate the improved effect of additive compositions comprisingpolyalkyl(methacrylate) based comb polymers according to the presentinvention on the Noack evaporation loss, corresponding additivecompositions of comb polymers in base oil were prepared and thecorresponding Noack evaporation losses at 250° C. were determined to CECL-40B. The results are outlined in Table 3.

TABLE 3 Noack evaporation losses of polymers in base oil (=additivecomposition A) polymer acrylate in the Oil A Oil B polymer content netpolymer (Group III) (DIOS) NOACK Additive # used [%] [Mol %] [%] [%] [%]A0 — — —  93.33  6.67 15.5 A1*⁾ Example 1 25 — 70.0 (+5% — 29.6Hydroseal) A2*⁾ Example 2 25 — 70.0 5.0 20.9 A3 Example 3 25 1.6 70.05.0 18.2 A4 Example 4 25 3.1 70.0 5.0 16.2 A5 Example 5 25 3.2 70.0 5.016.2 A6 Example 6 25 6.5 70.0 5.0 15.3 A7 Example 7 25 3.8 70.0 5.0 16.3A8 Example 8 25 7.5 70.0 5.0 15.4 A9 Example 9 25 14.9 70.0 5.0 15.6 A10Example 10 25 4.0 70.0 5.0 17.1 A11 Example 11 25 3.9 70.0 5.0 16.6A12*⁾ Example 12 25 — 70.0 5.0 21.2 A13 Example 13 25 3.6 70.0 5.0 16.8A14 Example 14 25 7.1 70.0 5.0 15.3 A15 Example 15 25 0.7 70.0 5.0 20.2A16 Example 16 25 1.4 70.0 5.0 18.7 A17 Example 17 25 3.7 70.0 5.0 16.0A18 Example 18 25 3.8 70.0 5.0 15.8 A19*⁾ Example 19 25 22.11 70.0 5.014.0 A20*⁾ Example 20 25 36.32 70.0 5.0 14.9 A21 Example 21 25 14.0570.0 5.0 14.8 A22*⁾ Example 22 25 20.93 70.0 5.0 14.3 A23*⁾ Example 2325 34.41 70.0 5.0 13.8 A24*⁾ Example 24 25 9.93 70.0 5.0 15.1*⁾comparative example

In Table 3 are shown additive compositions having polymer concentrationsof 25%. Apart from A1, there is always used the same oil mixture of OilA and Oil B in a ratio of 14:1.

Generally, the addition of polyalkyl(meth)acrylate polymers to a baseoil leads to an increased Noack. Table 3 shows that the base oil mixtureitself (additive composition A0) has a Noack of 15.5%. The addition of25% of e.g. Example 2 (additive composition A2) raises the Noack to29.6%.

From Table 3 it is visible that the Noack evaporation loss of theadditive compositions depends strongly on a) the base oil used (pleasesee Al and A2) and b) the polymer composition used, more specificallythe amount of acrylate in the polymer (please see A3-A11 and A13-A18).Regarding a), the influence of the base oil, the comparison of A1 and A2shows that with the addition of a base oil with higher boiling point,like e.g. DIOS, the Noack evaporation loss of the additive compositionwas reduced by 29% (see A2 compared to A1: A2 shows a Noack of 20.9%compared to 29.6% of A1. That means a reduction of 29%).

Moreover, it was found that changing the polymer composition byincorporation of acrylate units in the comb polymer surprisingly leadsto an additional reduction of Noack evaporation loss by 27% (see A2 andA6 or A14). In this case, an acrylate amount of about 7 mol % was usedand the Noack value of 15.3 approximately met the Noack of the pure baseoil mix without polymer additive (A0). This is an indication that atthis acrylate amount the contribution of the polymer to the Noackevaporation loss was minimized. Additionally, it can be seen thatalready very small amounts of acrylates (1.6 to 3.1 mol %) resulted in asignificant decrease of Noack by 13 to 22%. In general, the moreacrylate was incorporated in the comb polymer the lower the Noackevaporation loss was, independent of the type of acrylate used (C4 AA orC16/18 AA). Combining effects a) and b) leads to a total reduction ofNoack by up to 48%.

Table 3 also shows that the addition of more than about 10-11% of alkylacrylates does not give significant further improvement of Noackevaporation loss. But the addition of more than 10-11% of alkylacrylates does lead to other drawbacks in relation to formulationparameters. This will be shown further down in Tables 5 and 6.

To show the shear stability of the polyalkyl(meth)acrylate based combpolymers according to the present invention, the additive compositionsA1 to A18 as disclosed in table 3 above were mixed with a dilution oilto give an additive composition comprising 15% of the correspondingadditive composition. The PSSI values are outlined in the followingTable 4 together with the kinematic viscosity data of the additivecompositions.

TABLE 4 Data showing viscometrics and shear stability of 15% of theadditive composition of Table 3 comprising the comb polymers preparedaccording to the present invention. 15% additive product composition 15%addtive composition in Group III oil*⁾ Additive in Group III oil* after12.5 min sonic shear composition KV₁₀₀ KV₄₀ KV₁₀₀ KV₄₀ PSSI PSSI used[mm²/s] [mm²/s] VI [mm²/s] [mm²/s] VI 100° C. 40° C. A1**⁾ nd nd nd ndnd nd nd nd A2**⁾ 8.1 30.1 263 8.1 30.1 262 1.6 1.5 A3 7.9 30.6 250 7.930.5 248 1.6 2.0 A4 8.0 30.7 253 7.9 30.5 250 3.5 3.5 A5 9.4 32.0 3009.2 31.6 295 4.2 4.1 A6 9.1 31.9 288 8.8 34.2 281 6.4 4.8 A7 8.5 30.4278 8.4 30.2 276 2.2 2.6 A8 8.5 30.6 277 8.4 30.5 275 2.2 2.2 A9 7.930.7 247 7.9 30.6 245 1.7 1.2 A10 8.2 30.6 262 8.2 30.4 261 1.2 2.8 A118.9 30.4 298 8.9 30.3 296 1.7 1.6 A12**⁾ 7.7 29.7 249 7.7 29.7 248 1.11.4 A13 8.7 29.8 294 8.7 29.7 293 1.1 1.6 A14 8.7 30.6 294 nd nd nd ndnd A15 8.9 29.7 306 8.9 29.6 304 2.0 2.2 A16 8.7 29.8 293 8.6 29.7 2930.8 2.1 A17 8.8 29.6 302 8.7 29.5 300 2.3 2.8 A18 9.0 29.8 310 8.9 29.6308 2.4 3.2 *⁾Group III base oil mixture (NB 3043 and NB 3080 fromNeste) with KV₁₀₀ of 4.9 cSt **⁾comparative example nd not determined

Table 4 shows that all additive compositions achieved excellent PSSIvalues at 100° C. of below 7; and most additive compositions achievedeven lower PSSI values of not more than 3.

In addition, all additive compositions show KV₁₀₀ values in the range of7.9 to 9.4 mm²/s and KV₄₀ values in the range of 29.6 to 32 mm²/s, i.e.in very narrow ranges.

As this is due for the compositions comprising the working examples(Examples A3 to A11 and A13 to A18) as well as comparative Examples(Examples A1, A2 and A12), that means that comb polymers in general showvery high VIs.

It could be shown that the advantageous characteristics alreadydescribed in the state of the art for comb polymers are maintained withthe new comb polymers described herein, but can additionally be combinedwith an improved Noack.

Evaluation of VI Improvers in Formulations

To demonstrate the effect of polyalkyl(methacrylate) based comb polymersaccording to the present invention on the Noack evaporation loss oflubricating oil compositions different formulation examples B wereprepared and the corresponding Noack evaporation losses at 250° C. weredetermined to CEC L-40B. Formulations B were prepared by adding theadditives A1-A24 as described in Table 3 above.

TABLE 5 0W20 engine oil formulations B without DI package in Yubase 4 asbase oil Parameter B1*⁾ B2*⁾ B3 B4 B5 B6 B7 B8 B9 Additive A1 A2 A3 A4A5 A6 A7 A8 A9 used Additive 12.5 12.8 12.5 14.0 nd 12.5 12.6 12.6 14.4content [%] KV₁₀₀ 7.29 6.74 7.58 6.92 nd 7.63 7.00 6.98 6.91 [mm²/s]KV₄₀ 23.82 23.78 24.91 24.79 nd 25.31 23.82 23.97 24.97 [mm²/s] VI 303268 303 265 nd 300 285 281 262 CCS-35 — 3257 3324 3130 nd 3314 — 31643107 [mPas] Noack 15.4 14.6 14.4 14.6 nd 14.1 14.3 14.1 14.2 [%] HTHS₈₀6.37 6.51 6.61 6.68 nd 6.69 6.37 6.41 6.71 [mPas] HTHS₁₀₀ 4.44 4.50 4.754.69 nd 4.80 4.50 4.58 4.77 [mPas] HTHS₁₅₀ 2.62 2.59 2.61 2.63 nd 2.592.60 2.59 2.61 [mPas] Parameter B10 B11 B12*⁾ B13 B14 B15 B16 B17 B18Additive A10 A11 A12 A13 A14 A15 A16 A17 A18 used Additive 13.2 12.615.0 12.6 12.5 12.4 12.6 12.0 12.0 content [%] KV₁₀₀ 6.85 7.14 6.92 7.027.01 7.09 6.96 6.85 7.05 [mm²/s] KV₄₀ 24.26 23.83 24.52 23.48 23.5623.27 23.40 23.09 23.15 [mm²/s] VI 268 294 269 292 290 300 289 287 299CCS-35 3076 3196 3041 2986 3003 2992 2988 3007 3013 [mPas] Noack 14.614.1 14.6 14.5 14.2 14.3 14.3 14.1 14.2 [%] HTHS₈₀ 6.54 6.18 6.55 6.156.17 6.06 6.13 6.01 6.00 [mPas] HTHS₁₀₀ 4.58 4.57 4.79 4.45 4.51 4.304.38 4.28 4.24 [mPas] HTHS₁₅₀ 2.62 2.58 2.63 2.61 2.58 2.58 2.58 2.602.58 [mPas] Parameter B19*⁾ B20*⁾ B21 B22*⁾ B23*⁾ B24*⁾ Additive A19 A20A21 A22 A23 A24 used Additive 16.0 18.0 15.2 15.2 16.7 15.0 content [%]KV₁₀₀ 6.95 6.99 7.04 7.02 7.07 7.25 [mm²/s] KV₄₀ 26.24 27.54 25.34 25.3526.33 27.36 [mm²/s] VI 247 233 265 263 253 250 CCS-35 3273 3393 31263108 3188 3409 [mPas] Noack 13.8 14.2 14.0 13.9 13.9 14.0 [%] HTHS₈₀7.12 7.56 6.96 6.98 7.30 7.30 [mPas] HTHS₁₀₀ 5.07 5.26 5.03 5.05 5.185.12 [mPas] HTHS₁₅₀ 2.60 2.60 2.62 2.63 2.59 2.65 [mPas] *⁾comparativeexample nd not determined

Formulations with Yubase 4 as base oil were prepared by usingformulation targets 0W20 according to SAE J300; i.e. it was formulatedon an HTHS₁₅₀ target of 2.6 mPas. The resulting additive content wastypically between 12-15%. Characteristic EO formulation properties(KV₄₀, KV₁₀₀, CCS, HTHS₁₀₀, HTHS₈₀) were measured and are summarized inTable 5. Comparing the comparative examples B1, B2 and B12 with theworking examples shown in Table 5, a distinct decrease in Noack from15.4% (B1) and 14.6% in case of B2 or B12, to 14.6 to14.1% (B3 to B11and B13 to B18) is visible. It is also visible that the Noackevaporation loss of the engine oil formulations strongly depends on a)the base oil mix used in the additive composition (please see B1 and B2)and b) the polymer composition used in the additive composition, morespecifically the amount of acrylate in the polymer (please see B3 to B11and B13 to B18).

Using base oils with higher boiling point in the additive composition,like e.g. DIOS, the Noack evaporation loss of the engine oil formulationwas reduced by 5.2% (see B1 and B2). Moreover, it was found thatchanging the polymer composition in the additive composition byincorporation of acrylate units in the comb polymer surprisingly leadsto an additional reduction of Noack evaporation loss by 3.4% (see B2 andB6, B8, B11 or B17). Additionally, already very small amounts ofacrylates (<4 mol %) in the additive composition resulted in asignificant decrease of Noack in the engine oil formulation by 2.1 to3.4%. In general, the more acrylate was incorporated in the combpolymer, the lower the Noack evaporation loss of the engine oilformulation was. Combining effects a) and b) leads to a total reductionof Noack by 8.4%.

TABLE 6 overview of results and conclusions Monomers in net compositionacrylate Formulation Details C16/18 C4 Sum of in the net AdditivePolymer MM AA AA AA polymer Content Noack KV₄₀ HTHS₈₀ HTHS₁₀₀Formulation # used [wt %] [wt %] [wt %] [wt %] [Mol %] [wt %] [%] VI[mm²/s] [mPas] [mPas] B1*⁾ Ex. 1 22.51 — — 0 0 12.5 15.4 303 23.82 6.374.44 B2*⁾ Ex. 2 20.81 — — 0 0 12.8 14.6 268 23.78 6.51 4.50 B3 Ex. 321.19 2.56 — 2.56 1.6 12.5 14.4 303 24.91 6.61 4.75 B10 Ex. 10 21.191.94 1.94 3.88 4.0 13.2 14.6 268 24.26 6.54 4.58 B4 Ex. 4 21.37 5.11 —5.11 3.1 14.0 14.6 265 24.79 6.68 4.69 B5 Ex. 5 21.19 5.12 — 5.12 3.2 ndnd nd nd nd nd B6 Ex. 6 21.74 10.16 — 10.16 6.5 12.5 14.1 300 25.31 6.694.80 B24*⁾ Ex. 24 22.10 15.45 — 15.45 9.9 15.0 14.0 250 27.36 7.30 5.12B7 Ex. 7 21.00 — 2.56 2.56 3.8 12.6 14.3 285 23.82 6.37 4.50 B8 Ex. 821.56 — 5.09 5.09 7.5 12.6 14.1 281 23.97 6.41 4.58 B9 Ex. 9 22.10 —10.12 10.12 14.9 14.4 14.2 262 24.97 6.71 4.77 B19*⁾ Ex. 19 22.47 —15.10 15.10 22.1 16.0 13.8 247 26.24 7.12 5.07 B20*⁾ Ex. 20 22.47 —25.17 25.17 36.3 18.0 14.2 233 27.54 7.56 5.26 B12*⁾ Ex. 12 13.57 — — 00 15.0 14.6 269 24.52 6.55 4.79 B15 Ex. 15 13.57 — 0.51 0.51 0.7 12.414.3 300 23.27 6.06 4.30 B16 Ex. 16 13.57 — 1.02 1.02 1.4 12.6 14.3 28923.40 6.13 4.38 B13 Ex. 13 13.57 — 2.54 2.54 3.6 12.6 14.5 292 23.486.15 4.45 B17 Ex. 17 13.15 1.92 1.92 3.84 3.7 12.0 14.1 287 23.09 6.014.28 B18 Ex. 18 13.97 1.92 1.92 3.84 3.8 12.0 14.2 299 23.15 6.00 4.24B11 Ex. 11 13.84 1.93 1.93 3.86 3.9 12.6 14.1 294 23.83 6.18 4.57 B14Ex. 14 13.84 — 5.07 5.07 7.1 12.5 14.2 290 23.56 6.17 4.51 B21*⁾ Ex. 2114.49 — 10.06 10.06 14.1 15.2 14.0 265 25.34 6.96 5.03 B22*⁾ Ex. 2214.49 — 15.09 15.09 20.9 15.2 13.9 263 25.35 6.98 5.05 B23*⁾ Ex. 2314.74 — 25.08 25.08 34.4 16.7 13.9 253 26.33 7.30 5.18 *⁾comparativeexample nd not determined

Table 6 is a summary table showing certain data as already presented inTables 2-5 above. Therein are listed the formulations B by theirincreasing acrylate content and the resulting formulation details.

It is visible that an increased acrylate content negatively influencesthe formulation performance. In all cases the VI is decreasing with veryhigh acrylate content of above 11% by weight. The HTHS₈₀ and HTHS₁₀₀ aswell as KV₄₀ are increasing and the treat rate is becoming very high. Atthe same time the Noack stays more or less constant and does not improvesignificantly anymore.

From US 2010/0190671 it is known that low KV₄₀, HTHS₈₀ and HTHS₁₀₀values are necessary to achieve good fuel economy (see page 1, paragraph[0005] of US 2010/0190671). That means that the lubricating oilformulations according to the present invention can also be used todecrease fuel consumption.

TABLE 7 0 W 8 engine oil formulation with DI package in Yubase 3 as baseoil (Formulation Examples C) Product C1 C2 additive composition A1 [%]2.5 additive composition A8 [%] 3 OLOA 55501 8.9 8.9 Yubase 3 88.6 88.1Sum 100 100 Tests KV₁₀₀ [mm²/s] 4.44 4.50 KV₄₀ [mm²/s] 17.24 17.56 VI183 183 CCS-35 [mPas] 1825 1796 Noack [%] 36.6 36.2 HTHS₈₀ [mPas] 4.814.90 HTHS₁₀₀ [mPas] 3.29 3.45 HTHS₁₅₀ [mPas] 1.69 1.72

Formulations with Yubase 3 as base oil and OLOA 55501 as DI package wereprepared by using formulation targets of 0W8 according to SAE J300; i.e.it was formulated on an HTHS₁₅₀ target of 1.7 mPas. The resultingadditive content was typically between 2.5 to 3%. Characteristic engineoil formulation properties (KV₄₀, KV₁₀₀, CCS, HTHS₁₀₀, HTHS₈₀) weremeasured and are summarized in Table 7.

It was found that changing the base oil composition and the polymercomposition in the additive composition by incorporating acrylate unitssurprisingly leads to a reduction of Noack evaporation loss by 1.1% (seeC1 and C2).

TABLE 8 0W 20 engine oil formulation with DI package in different baseoil mixtures (Formulation Examples D) Product [%] D1 D2 D3 D4 D5 D6 D7D8 additive 9.7 8.3 composition A1 additive 10.4 10.5 8.2 8.5composition A8 additive 8.3 8.5 composition A7 OLOA 55501 8.9 8.9 8.98.9 8.9 8.9 8.9 8.9 Base Oil Mix 1* 81.4 80.7 Base Oil Mix 2* 80.6 BaseOil Mix 3* 82.8 82.9 82.8 Base Oil Mix 4* 82.6 82.6 Sum 100 100 100 100100 100 100 100 Tests KV₁₀₀ 7.22 7.22 7.16 7.51 7.24 7.29 7.25 7.29[mm²/s] KV₄₀ 27.09 27.72 27.07 28.82 28.77 28.63 28.43 28.27 [mm²/s] VI252 244 249 247 233 238 237 242 CCS-35 3081 3161 3015 4508 4559 45994383 4425 [mPas] Noack 14.3 12.8 14.3 15.7 14.0 14.3 15.4 15.2 [%]HTHS₈₀ 6.92 7.03 6.94 7.20 7.24 7.25 7.20 7.17 [mPas] HTHS₁₀₀ 4.72 4.884.82 4.95 5.02 4.95 5.00 4.92 [mPas] HTHS₁₅₀ 2.60 2.65 2.60 2.62 2.612.60 2.57 2.60 [mPas] *Base Oil Mix 1 = 5% GTL3 + 95% GTL 4 *Base OilMix 2 = 10% GTL3 + 90% GTL4 *Base Oil Mix 3 = 5% Yubase 3 + 95% Yubase 4*Base Oil Mix 4 = 10% Yubase 3 + 90% Yubase 4

Formulations with mixtures of GTL3 and GTL4 as well as with mixtures ofYubase 3 and Yubase 4 as base oils and OLOA 55501 as DI package wereprepared by using formulation targets 0W20 according to SAE J300; i.e.it was formulated on a HTHS₁₅₀ target of 2.6 mPas. The resultingadditive content was typically between 8.2 to 10.5% by weight.Characteristic engine oil formulation properties (KV₄₀, KV₁₀₀, CCS,HTHS₁₀₀, HTHS₈₀) were measured and are summarized in Table 8. It wasfound that changing the base oil composition and the polymer compositionin the additive composition by incorporating acrylate units (A8)surprisingly leads to a reduction of Noack evaporation loss by 10.5%(see D1and D2) with GTL3 and GTL4 as base oil mixture and by 10.8% (seeD4 and D5) with Yubase 3 and Yubase 4 as base oil mixture. This wayNoack values of 12.8 instead of 14.3% with GTL3 and GTL4 as base oilmixture and Noack values of 14.0 instead of 15.7% with Yubase 3 andYubase 4 as base oil mixture were obtained. This example demonstrateshow Noack levels of engine oil formulations can be reduced below therequired levels of 15% by using additive compositions comprisingacrylate monomers as described in this patent.

Moreover, the decrease in Noack leads to increased formulation optionslike the possibility of increasing the amount of low viscous base oilsin the formulation. For example, the amount of Yubase 3 or GTL3 in theformulation can be doubled and at the same time the obtained Noack iswell below 15% (see D3) or close to 15% (see D7, D8). The latter enablesthe increase of VI improver amount in the formulation leading toimproved performance (e.g. higher VI of the formulation, please compareD2 and D3 or D6 and D8) and therefore better fuel economy is expected.These examples demonstrate how a decreased Noack of the VII indirectlyleads to formulation options that would not have been possible otherwiseand which result in an improved performance of the engine oilformulation (higher VI).

1. A polyalkyl(meth)acrylate based comb polymer, comprising thefollowing monomers: 10 to 25% by weight of at least one ester of(meth)acrylic acid and a hydroxylated hydrogenated polybutadiene and (b)0.5% to 11% by weight of at least one C₄₋₁₈ alkyl acrylate.
 2. Thepolyalkyl(meth)acrylate based comb polymer according to claim 1,comprising the following monomers: (a) 10 to 25% by weight of at leastone ester of (meth)acrylic acid and a hydroxylated hydrogenatedpolybutadiene; (b) 0.5% to 11% by weight of at least one C₄₋₁₈ alkylacrylates acrylate; (c) 0% to 1% by weight of methyl methacrylate; (d)55% to 70% by weight of n-butyl methacrylate; (e) 5% to 20% by weight ofat least one C₁₀₋₁₅ alkyl methacrylate; and (f) 0% to 2% by weight ofstyrene monomers.
 3. The polyalkyl(meth)acrylate based comb polymeraccording to claim 1, comprising as component (b) 0.5 to 5% by weight,of at least one C₄₋₁₈ alkyl acrylate.
 4. The polyalkyl(meth)acrylatebased copolymer according to claim 1, having a weight-average molecularweight M_(w) in the range of 200,000 to 800,000 g/mol, determined bysize exclusion chromatography (SEC) using commercially availablepolymethylmethacrylate standards.
 5. The polyalkyl(meth)acrylate basedcopolymer according to claim 1, wherein the hydroxylated. hydrogenatedpolybutadiene of component (a) has a number-average molecular weightM_(n) to DIN 55672-1 of 4,000 to 6,000 g/mol.
 6. Thepolyalkyl(meth)acrylate based copolymer according to claim 1, having aPSSI of not more than 7, calculated according to ASTM D 6022-01 based ondata measured according to ASTM D 2603-B.
 7. A method of reducing Noackevaporation loss of a lubricating oil composition, the methodcomprising: applying the polyalkyl(meth)acrylate based comb polymer ofclaim 1 to a lubricating oil composition in need thereof.
 8. An additivecomposition, comprising: (A) 60 to 80% by weight of a base oil, and (B)20 to 40% by weight of a polyalkyl(meth)acrylate based comb polymer,comprising the following monomers: (a) 10 to 25% by weight of at leastone ester of (meth)acrylic acid and a hydroxylated hydrogenatedpolyhutadiene; and (b) 0.5% to 11% by weight of at least one C₄₋₁₈ alkylacrylate.
 9. The additive composition according to claim 8, comprising:(A) 60 to 80% by weight of a base oil; and (B) 20 to 40% by weight of apolyalkyl(meth)acrylate based comb polymer, comprising the followingmonomers: (a) 10 to 25% by weight of at least one ester of (meth)acrylicacid and a hydroxylated hydrogenated polybutadiene; (b) 0.5% to 11% byweight of at least one C₄₋₁₈ alkyl acrylate; (c) 0% to 1% by weight ofmethyl methacrylate; (d) 55% to 70% by weight of n-butyl methacrylate;(e) 5% to 20% by weight of at least one C₁₀₋₁₅ alkyl methacrylate; and(f) 0% to 2% by weight of at least one styrene monomer.
 10. The additivecomposition according to claim 8, having a VI of at least
 245. 11. Theadditive composition according to claim 8, wherein component (A) ispresent in an amount of 70 to 75% by weight and component (B) is presentan amount of 25 to 30% by weight.
 12. The additive composition accordingto claim 8, wherein component (A) comprises: (A1) 54 to 80% by weight ofat least one base oil selected from the group consisting of API Group Ioils, Group II oils, Group III oils. Group IV oils and any mixturethereof, and (A2) 0 to 6% by weight of at least one API Group V oil,based on the total weight of the additive composition.
 13. A method ofreducing Noack evaporation loss of a lubricating oil compositioncompositions the method comprising: applying the additive composition ofclaim 8 to a lubricating oil composition in need thereof.
 14. Alubricating oil composition, comprising: (A) 75 to 99.5% by weight of abase oil; (B) 0.5 to 10% by weight of a polyalkyl(meth)acrylate basedcomb polymer, comprising the following monomers: (a) 10 to 25% by weightof at least one ester of (Ineth)acrylic acid and a hydroxylatedhydrogenated polybutadiene; (b) 0.5% to 11% by weight of at least oneC₄₋₁₈ alkyl acrylate; and (C) 0 to 15% by weight of one or more furtheradditives.
 15. The lubricating oil composition according to claim 14,comprising: (A)75 to 99,5% by weight of a base oil; (B) 0.5 to 10% byweight of a polyalkyl(meth)acrylate based comb polymer, comprising thefollowing monomers: (a) 10 to 25% by weight of at least one ester of(meth)acrylic acid and a hydroxylated hydrogenated polybutadiene; (b)0.5% to 11% by weight of at least one C₄₋₁₈ alkyl acrylate; (c) 0% to 1%by weight of methyl methacrylate; (d) 55% to 70% by weight of n-butylmethacrylate; (e) 5% to 20% by weight of at least one C₁₀₋₁₅ alkylmethacrylate; (f) 0% to 2% by weight of at least one styrene monomer;and (C) 0 to 15% by weight of one or more further additives.
 16. Thelubricating oil composition according to claim 14, wherein component (A)comprises: (A1) 74.25 to 99.45% by weight of at least one base oilselected from the group consisting of API Group I oils. Group II oils,Group III oils, Group IV oils and any mixture thereof, and (A2) 0.05 to0.75% by weight of at least one API Group V oil. based on the totalweight of the lubricating oil composition.
 17. The lubricating oilcomposition according to claim 14, wherein component (C) is at least oneselected from the group consisting of conventional VI improvers,dispersants, defoamers, detergents, antioxidants, pour pointdepressants, antiwear additives, extreme pressure additives, frictionmodifiers, anticorrosion additives, dyes and any mixtures thereof. 18.The polyalkyl(meth)acrylate based copolymer according to claim 1, havinga weight-average molecular weight in the range of 300,000 to 600,000g/mol, determined by size exclusion chromatography (SEC) usingcommercially available poly methylmethacrylate standards.
 19. Thepolyalkyl(meth)acrylate based copolymer according to claim 1, having aPSSI of below 3, calculated according to ASTM D 6022-01 based on datameasured according to ASTM D 2603-B.
 20. The additive compositionaccording to claim 8, wherein component (A2) comprises dioctylsehacate(DIOS).